The present invention relates to a two-dimensional charge-coupled device (CCD) image sensor which is used in an image-picking-up apparatus such as a TV camera and a VTR camera, and more specifically, to a method of driving an interline-transfer type CCD image sensor.
The two-dimensional CCD image sensor, which is now finding applications in TV cameras and in VTR cameras, includes an imaging area (photosensitive area) having a plurality of rows of light-sensing elements which accumulate electrical charges of amounts corresponding to intensity of irradiated lights for a predetermined period of time, a storage area (memory area) having a plurality of shift registers each receiving the accumulated charges from each row of the imaging area and storing them, and a readout register receiving the stored charges from each shift register and outputting a video signal. Such a CCD image sensor is disclosed in the U.S. Pat. No. 4,322,753 assigned to the same assignee. In operation of such CCD image sensor, the period of time of the charge accumulation in each light-sensing row in the imaging area is fixed to one television field time, which corresponds to 1/60 second exposure time in a mechanical shutter of a camera. When a quickly moving object is picked-up, therefore, a fuzzy video signal is produced to deteriorate the resolution. In order to remove such defect, it is necessary that the CCD image sensor has a shutter function of more than 1/60 second and up to 1/2000 second exposure time. For this purpose, it has been attempted to provide a mechanical shutter in front of the CCD image sensor. However, the camera becomes bulky and the manufacturing cost increases.